Greg Mowry

Design and performance of diffractive optics for custom laser resonators

Diffractive optical elements are used as end mirrors and internal phase plates in an optical resonator. A single diffractive end mirror is used to produce an arbitrary real-mode profile, and two diffractive mirrors are used to produce complex profiles. Diffractive mirror feature size and phase quantization are shown to affect the shape of the fundamental mode, the fundamental-mode loss, and the discrimination against higher-order modes. Additional transparent phase plates are shown to enhance the modal discrimination of the resonator at the cost of reduced fabrication tolerances of the diffractive optics. A 10-cm-long diffractive resonator design is shown that supports an 8.5-mm-wide fundamental mode with a theoretical second-order mode discrimination of 25% and a negligible loss to the fundamental mode.

External diode-laser-array cavity with mode-selecting mirror

A new external optical cavity employing a mode‐selecting mirror is used to tailor the amplitude and phase of the fundamental array mode and discriminate between higher‐order modes. We explore the ability of this phase‐coded mirror to select a particular mode and compare it with a conventional Talbot cavity. Diffraction‐limited performance of the in‐phase fundamental mode is shown.

Modal analysis of a Talbot cavity

Modal analyses of Talbot cavity eigenmodes are performed for a finite diode laser array using a simple finite external mirror and a patterned external mirror. At a full round‐trip Talbot length, the in‐phase and oscillating‐phase modes of the cavity with a simple flat mirror have slightly different thresholds. The increased modal separation from a patterned‐mirror Talbot resonator is shown to be larger than a flat‐mirror resonator with a round‐trip distance of half a Talbot length. In all these cases, steady‐state oscillation is shown to consist of either the in‐phase or oscillating‐phase mode. The inherent flaw of the Talbot resonator suggested by P. Latimer [Appl. Phys. Lett. 62, 217 (1993)] is thus shown to be a simple matter of modal separation rather than a ‘‘violation of the widespread assumption of grating self‐imaging.’’

Modal properties of an external diode-laser-array cavity with diffractive mode-selecting mirrors

Coupled mode theory is used to describe the behavior of an external laser cavity consisting of a diode laser array and a diffractive mode-selecting mirror. The mirror is designed to establish a uniform-amplitude, uniform-phase fundamental mode. Coupled mode theory is then used to study the behavior of higher-order modes. We show that the maximum discrimination against higher-order modes occurs when the round-trip cavity length satisfies certain Talbot relations. In addition, this high modal discrimination can be maintained for arrays with large numbers of lasers without incurring significant loss in the fundamental mode.

Large‐area, single‐transverse‐mode semiconductor laser with diffraction‐limited super‐Gaussian output

An external cavity semiconductor laser that incorporates a large‐area amplifier has been successfully stabilized into a single transverse mode over the 600 μm width of the amplifier. Single‐transverse‐mode operation is achieved by using the combination of a diffractive mode‐selecting mirror and an aperture. 2.8 W of stable diffraction‐limited output power is achieved.

Novel Laser Beam Shaping and Mode Control with Diffractive Optical Elements

Diffractive optical elements are shown in this review paper to provide additional flexibility in laser resonator design. Diffractive end mirrors allow the designer to tailor the mode profile of the laser. Additional intracavity diffractive elements increase the discrimination against higher-order modes. Experimental results are shown for Nd:YAG lasers and wide-stripe diode lasers.

Modal properties of laser arrays using diffractive mode-selecting mirrors

The modal properties of a laser resonator consisting of an array of sources and a diffractive mode-selecting mirror are presented. The modal discrimination is optimized by selection of cavity parameters, and can be enhanced by additional diffractive elements. We find that the modal properties differ significantly from a conventional Talbot cavity. Because of the diffractive mode-selecting mirror, these are virtually no edge effects and the fundamental mode loss is very small. The modal discrimination is maximized at a round-trip cavity length of both one-half and one Talbot distance. There is an optimum array fill factor that depends on the cavity length and the array size. Finally, if the cavity length and fill factor are optimized, there is no loss of discrimination with increasing numbers of elements in the array.

Advances in diffractive optical laser resonators

Diffractive optics are employed as cavity mirrors and intracavity elements in advanced laser resonator designs. The diffractive elements are used to produce custom fundamental mode shapes, discriminate against higher-order modes, and correct thermal aberrations in laser crystals.

Applications of diffractive optics to diode laser arrays and amplifiers

This paper reviews applications of diffractive optics to optical resonators using diode laser arrays and wide-stripe diode-laser amplifiers as the gain medium. The mode profile can be tailored to any desirable shape by proper design of the diffractive optics. By optimizing additional cavity parameters, these resonators can be designed to discriminate against higher- order cavity modes, insuring single-spatial-mode operation. As a first example, we show a diffractive laser mirror designed to excite a uniform-intensity supermode of an AlGaAs laser array. The effect of varying the phase of this array on modal discrimination is studied. In the second example, a laser mirror is designed to produce a super-Gaussian beam profile in a wide-stripe semiconductor laser amplifier. Two-and-eight-tenths watts of diffraction-limited optical power is obtained.